如何打印Argparse主解析器的帮助（使用）部分而不是子解析器的使用？

我已经用Argparse编写了命令行程序已有一段时间了，我试图以这样的方式编写它：当用户向命令行提供以下内容时：

$python my_script.py -h

将打印出一个帮助部分（用法），该部分将打印出主解析器的帮助部分，以及子解析器的简要概述。

但是现在，每当我在终端中输入上一行时，我都不会使用它，而是会得到大量的回溯和以下错误：

TypeError: expected string or buffer

我以前从未使用基于argparse的命令行程序发生此错误。此外，如果我提供了一个次级解析器的名称，

$python my_script.py subparserA -h

我得到了子解析器用法的打印输出。其他次级解析器也是如此。

那么，为什么我无法获得主解析器的用法？这以前对我有用，所以我不知道为什么现在不起作用。我真的希望用户能够查看可用的不同子解析器的概述。

目前，我的基本代码是通过以下方式设置的：

import argparse
import sys

if __name__ == "__main__":
    Parser = argparse.ArgumentParser(prog= "My_program")

    Parser.description= "This program does A and B things."
    subparsers= Parser.add_subparsers(help= "SubparserA does A things and SubparserB does B things", dest='mode')

    subparserA= subparsers.add_parser("subparserA", help= "Additional explanation of what A things entail")

    subparserA.add_arguments("-foo", required=True, help= "foo is needed for SubparserA to work")

    subparserB= subparsers.add_parser("subparserB", help="Additional explanation of what B things entail")

    subparserB.add_argument("-bar", required=True, help= "bar is needed for SubparserB to work")

    args= Parser.parse_args()

    if args.mode == "subparserA":
        ###do things pertinent to subparserA
    elif args.mode== "subparserB":
        ###do things pertinent to subparserB
    else:
        argparse.print_help()
        argparse.ArgumentError("too few arguments")

更新

这是错误的完整回溯：

Traceback (most recent call last):
  File "my_program.py", line 164, in <module>
    args= Parser.parse_args()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 1701, in parse_args
    args, argv = self.parse_known_args(args, namespace)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 1733, in parse_known_args
    namespace, args = self._parse_known_args(args, namespace)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 1939, in _parse_known_args
    start_index = consume_optional(start_index)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 1879, in consume_optional
    take_action(action, args, option_string)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 1807, in take_action
    action(self, namespace, argument_values, option_string)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 996, in __call__
    parser.print_help()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 2340, in print_help
    self._print_message(self.format_help(), file)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 2314, in format_help
    return formatter.format_help()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 281, in format_help
    help = self._root_section.format_help()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 211, in format_help
    func(*args)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 485, in _format_text
    return self._fill_text(text, text_width, indent) + '\n\n'
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 621, in _fill_text
    text = self._whitespace_matcher.sub(' ', text).strip()
TypeError: expected string or buffer